Study On The Lattice Anisotropy And Deformation Mechanism Of Fe-18Mn-1.3Al-0.6C High Manganese TWIP Steel

Among the second-generation high-strength steels,twin-induced plasticity(TWIP)steel has become one of the most promising new automotive steels in the process of automotive light-weighting due to its excellent properties of high strength,high plasticity,high energy absorption and high strain hardening rate.The material studied in this paper is a third generation TWIP steel with an alloy composition of Fe-18Mn-1.3Al-0.6C,using hardness tests and tensile experiments,combined with characterization by optical microscopy(OM),scanning electron microscopy(SEM),X-ray diffraction(XRD),electron backscatter diffraction(EBSD)and transmission electron microscopy(TEM),focusing on the effect of different plastic deformation methods and different grain sizes on the strengthening mechanisms of experimental steels,explored the connection between microstructure evolution and mechanical properties to reveal the effects of different plastic deformation methods on the lattice plastic strain and lattice anisotropy of TWIP steels,and the strengthening mechanism caused by the interaction of dislocation multiplication and twinning behavior.As well as the work-hardening behavior of experimental steels with different grain sizes under rolling predeformation as influenced by twinning and strain distribution.The following study results were obtained.After plastic deformation,the Fe-18Mn-1.3Al-0.6C steel is still single-phase austenite organization,and no martensitic phase transformation due to plastic strain has occurred.The plastic lattice strain of the unidirectional tensile,unidirectional rolled and cross-rolled samples gradually increased with the increase of the strain,but the plastic lattice strain of the crossrolled samples was smaller than that of the unidirectional rolled samples at different rolling reduction,and the degree of work hardening was lower,so the Vickers hardness of the samples was lower.The dislocation density of cross-rolled rolls increases rapidly with the increase in the amount of reduction,and the dislocation strengthening makes the tensile strength of the samples of the two rolling methods similar.At the same time,cross-rolling can effectively promote twinning and activate the secondary twin system,which makes the twin become the main bearer of plastic strain,playing a stronger obstructive effect on dislocation movement,enhancing the TWIP effect,and reducing the generation of texture during plastic deformation,reducing plastic lattice anisotropy,making the grain orientation more uniform,and thus obtaining better plasticity.The hardening behavior of annealed samples with different grain sizes is significantly different after different pre-deformation.Since the critical nucleation stress of mechanical twinning decreases with the increase of grain size,the plastic strain of large-size grain samples can effectively promote the generation and growth of twins in plastic strain,resulting in an obvious TWIP effect,and inhibit the growth of dislocations.The continuous contribution of dislocation strengthening and twinning leads to a longer plateau period in the work-hardening rate curve,and increases the work-hardening index and work-hardening capacity,and makes the strain uniformly distributed at the grain boundaries and twin boundaries inside the grain,effectively relieving the stress concentration at the grain boundaries and improving the plasticity of the sample.